The present invention relates to the provision of protective oxide layers on alloys.
While oxides form naturally on most alloys (e.g., iron and nickel oxides on steels), the oxides most commonly formed in this way are a mere nuisance and of little value in protecting the underlying alloy. An example of the necessity of a protective layer can be found in the stainless steel cathodes employed in apparatus for the electroformation of metallic strands. Such cathodes are discussed in U.S. Pat. No. 3,929,610, issued Dec. 30, 1975, entitled "Electroformation of Metallic Strands", owned by the assignee of the present application, and incorporated herein by reference.
As discussed in that patent, epoxy or other electrically insulated material is used as a coating on a stainless steel cathode to provide insulation and protection against the corrosive acid solution and to allow electrodeposition of metals (e.g., Cu) at the unprotected cathode areas. Eventual failure of the cathode often occurs at the bond between the stainless steel and the epoxy. It is believed that the conventional oxides which exist on the stainless steel surfaces and are not resistant to acid contribute to such cathode failure.
It has been proposed to coat the stainless steel with oxides such as Al.sub.2 O.sub.3 before application of the epoxy. Such coatings, however, tend to crack during actual use due to differences in thermal expansion characteristics between the underlying material (e.g., stainless steel) and the applied oxide coating.
In view of the foregoing, it is a principal object of the present invention to provide an improved technique for achieving a protective oxide layer on an alloy.
Another object is to provide a method of furnishing an acid resistant oxide coating on a large number of different alloys.
Yet another object of the invention is to provide a durable and acid resistant oxide layer on stainless steel alloys.